Electron gun power supply and monitoring controller

Note: This project is designed for a particular experiment so it will not be much of use for anyone who's not working on exactly that experiment.

This is firmware for a simple electron gun controller that is controlling

• Up to four FUG HCP 14-6500 high voltage power supplies (acceleration voltage, Wehnelt cylinder, focus voltage and a single deflection voltage power supply)
• The voltage and current measured by FUG HCP 14-6500 can also be used for general monitoring and beam loss measurement

External communication ports

• UART0 provides main communication interface (and is also used by avrdude during flashing - there is an Arduino bootloader flashed on the board so flash method ẁiring can be used via USB

• Other UARTs may be used for RS485 or other components later on

Pin assignment

Pin	Assignment	Mode	ATEMGA2560 Port / Pin
22	PSU1: Output enable	Digital out (optocoupled)	PA0
23	PSU1: Polarity set	Digital out (optocoupled)	PA1
24	PSU1: Current control mode	Digital in	PA2
25	PSU1: Voltage control mode	Digital in	PA3
42	PSU1: Voltage set	Analog out	PL7
43	PSU1: Current limit set	Analog out	PL6
A0	PSU1: Voltage sense	Analog in	PF0
A1	PSU1: Current sense	Analog in	PF1
26	PSU2: Output enable	Digital out (optocoupled)	PA4
27	PSU2: Polarity set	Digital out (optocoupled)	PA5
28	PSU2: Current control mode	Digital in	PA6
29	PSU2: Voltage control mode	Digital in	PA7
44	PSU2: Voltage set	Analog out	PL5
45	PSU2: Current limit set	Analog out	PL4
A2	PSU2: Voltage sense	Analog in	PF2
A3	PSU2: Current sense	Analog in	PF3
30	PSU3: Output enable	Digital out (optocoupled)	PC7
31	PSU3: Polarity set	Digital out (optocoupled)	PC6
32	PSU3: Current control mode	Digital in	PC5
33	PSU3: Voltage control mode	Digital in	PC4
46	PSU3: Voltage set	Analog out	PL3
47	PSU3: Current limit set	Analog out	PL2
A4	PSU3: Voltage sense	Analog in	PF4
A5	PSU3: Current sense	Analog in	PF5
34	PSU4: Output enable	Digital out (optocoupled)	PC3
35	PSU4: Polarity set	Digital out (optocoupled)	PC2
36	PSU4: Current control mode	Digital in	PC1
37	PSU4: Voltage control mode	Digital in	PC0
48	PSU4: Voltage set	Analog out	PL1
49	PSU4: Current limit set	Analog out	PL0
A6	PSU4: Voltage sense	Analog in	PF6
A7	PSU4: Current sense	Analog in	PF7
38	Filament power supply (230V side)	Digital out	PD7
A8	Current sensor for filament	Analog in	PK0
50	AD7705 MISO	Digital in	PB3
51	AD7705 MOSI	Digital out	PB2
52	AD7705 SCK	Digital out	PB1
53	AD7705 CS	Digital out	PB0
PWM10	AD7705 Reset	Digital out	PB4
PWM11	AD7705 data ready	Digital in	PB5

Protocol

In contrast to other implementations this board supports an ASCII based communication protocol. For synchronization all messages start with a fixed synchronization pattern consisting of three dollar signs. Each command is terminated via a CR LF or only LF (CR is simply ignored by the serial parser). Numbers are transmitted as ASCII decimal numbers.

Command	Sequence	Response	Status
ID	$$$ID	Sends a simple ID response that identifies the firmware (ex. $$$electronctrl_20210707_001<LF>)	working, tested
Filament on	$$$FILON	Switches filament power supply on	working, tested
Filament off	$$$FILOFF	Switches filament power supply off	working, tested
Estimate beam current	$$$BEAMA	Calculates estimated beam current in 1/10 of microamperes
Beam on	$$$BEAMON	Switches beam high voltage on (slowly, performing insulation test)	working, tested
Beam HV off	$$$BEAMHVOFF	Switches beam high voltage off	working, tested
Get PSU current	$$$PSUGETA[n]	Gets current for power supply 1,2,3,4	working, tested
Get PSU voltage	$$$PSUGETV[n]	Gets voltage for power supply 1,2,3,4	working, tested
Get PSU modes	$$$PSUMODE	Gets the mode for each PSU as a sequence of 4 ASCII chars (A or V for current or voltage controled mode, - for disabled)	working, tested
Set PSU current limit	$$$PSUSETA[n][mmm]	Sets the power supply current limit for one of the 4 PSUs. The limit is supplied in 1/10 of an microampere	working, tested
Set PSU target voltage	$$$PSUSETV[n][mmm]	Sets the power supply voltage for one of the 4 PSUs. The voltage is set in V	working, tested
Set PSU polarity	$$$PSUPOL[n][p/n]	Sets the polarity to be positive or negative	working, tested
Set PSU output enable	$$$PSUON[n]	Enabled the output of the given PSU	working, tested
Set PSU output disable	$$$PSUOFF[n]	Disabled the output of the given PSU	working, tested
Disable all voltages (PSU and filament)	$$$OFF	Disabled all voltages including the filament supply	working, tested
Get filament voltage	$$$FILV	Measures filament voltage (if supported)
Get filament current	$$$FILA	Measures filament current (if supported)
Set filament current	$$$SETFILA[n]	Sets filament current via current controller board
Perform HV insulation test	$$$INSUL	Performs insulation test. Reports voltages while testing.	working, tested
Perform cathode bakeout	$$$FILBAKE	Performs a baking sequence on filament to remove any residue of trapped gas on the surface
Perform software reset	$$$RESET	Performs a software reset on the control system (reinitializes everything, no power cycle)